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The therm (symbol, thm) is a non- SI unit of heat energy equal to 100,000
British thermal unit The British thermal unit (BTU or Btu) is a unit of heat; it is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. It is also part of the United States customary units. The modern SI u ...
s (BTU), and approximately
megajoules The joule ( , ; symbol: J) is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force applied ...
,
kilowatt-hours A kilowatt-hour ( unit symbol: kW⋅h or kW h; commonly written as kWh) is a unit of energy: one kilowatt of power for one hour. In terms of SI derived units with special names, it equals 3.6 megajoules (MJ). Kilowatt-hours are a common bil ...
, kilocalories and
thermie A thermie (th) is a non- SI metric unit of heat energy, part of the metre-tonne-second system sometimes used by European engineers. The thermie is equal to the amount of energy required to raise the temperature of of water at at standard atmosp ...
s. One therm is the energy content of approximately of
natural gas Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbon di ...
at standard temperature and pressure. However, the BTU is not standardised worldwide, with slightly different values in the EU, UK, and USA, meaning that the energy content of the therm also varies by territory. Natural gas meters measure volume and not energy content, and given that the energy density varies with the mix of hydrocarbons in the natural gas, a 'therm factor' is used by natural gas companies to convert the volume of gas used to its heat equivalent, usually being expressed in units of 'therms per CCF' (CCF is an abbreviation for 100 cubic feet). Higher than average concentration of ethane, propane or
butane Butane () or ''n''-butane is an alkane with the formula C4H10. Butane is a gas at room temperature and atmospheric pressure. Butane is a highly flammable, colorless, easily liquefied gas that quickly vaporizes at room temperature. The name bu ...
will increase the therm factor and the inclusion of non - flammable impurities, such as carbon dioxide or nitrogen will reduce it. The
Wobbe Index The Wobbe index (WI) or Wobbe number is an indicator of the interchangeability of fuel gases such as natural gas, liquefied petroleum gas (LPG), and town gas and is frequently defined in the specifications of gas supply and transport utilities. If ...
of a fuel gas is also sometimes used to quantify the amount of heat per unit volume burnt.


Definitions

* Therm (EC) ≡ BTUISO *: = joules *: ≈
kWh A kilowatt-hour ( unit symbol: kW⋅h or kW h; commonly written as kWh) is a unit of energy: one kilowatt of power for one hour. In terms of SI derived units with special names, it equals 3.6 megajoules (MJ). Kilowatt-hours are a common ...
*: The therm (EC) is often used by engineers in the US. * Therm (US) ≡ BTU59°F *: = joules *: ≈ kWh. * Therm (UK) ≡ joules *: ≡ kWh 10 therms are known as a decatherm (sometimes, dekatherm; commonly abbreviated Dth), which is BTU or 1 MMBTU (of whichever type). Further common abbreviations are MDth for a decatherms, and MMDth for decatherms.


Usage

United Kingdom regulations were amended to replace therms with joules with effect from 1999, with natural gas usually retailed in the derived unit, kilowatt-hours. Despite this, the wholesale UK gas market trades in therms. In the United States, natural gas is commonly billed in CCFs (hundreds of cubic feet) or therms.


Carbon footprint

According to the
EPA The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it be ...
burning one therm of natural gas produces on average of carbon dioxide.epa.gov "Greenhouse Gases Equivalencies Calculator - Calculations and References''
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See also

*
Barrel of oil equivalent The barrel of oil equivalent (BOE) is a unit of energy based on the approximate energy released by burning one barrel (, or ) of crude oil. The BOE is used by oil and gas companies in their financial statements as a way of combining oil and natur ...
* * Cubic mile of oil


References

{{Reflist Units of energy